The invention relates to apparatus and a method for conditioning polishing pads, and restoring the surface texture of a polishing pad.
During the process of manufacturing a memory disk, double-sided polishing is used to remove unwanted material from opposite sides of a substrate, typically of aluminum, nickel phosphorous or glass, and to produce a flat, smooth surface. Polishing of memory disks generally takes the form of double-sided polishing wherein a chemically active, abrasive-containing slurry is used in conjunction with two polishing pads. In a typical arrangement a polishing pad is adhered to each, an upper and a lower rotatable platen. The workpieces are held in a relative position by carriers which are placed between the pads. The slurry is fed onto the surface of the polishing pads. Polishing is affected by rotating the platens and the disks relative to each other, with the slurry generally dispensed throughout the polishing step of the cycle.
During the polishing process, properties of the polishing pads change. The pore structure of the polishing pad surface wears down, and the surface of the pad becomes smooth as a result of polishing byproducts, such as removed substrate material, becoming embedded in the surface. This results in a polishing surface which substantially reduces polishing performance. To restore the pads"" polishing performance, the pads are conditioned.
Conditioning is a technique wherein a polishing pad is treated typically between polishing cycles to restore its properties and thereby restore its polishing performance. Traditional pad conditioning involves the use of brushes to wipe the pad surface free of debris. However, the traditional method breaks down the pore walls due to intrusion into the pore structure from the bristles.
Prior to the invention, a polishing pad was conditioned by brushing with bristles to remove polishing debris imbedded in the pad, and to clean the pores of the pad. The pores of a poromeric polishing layer become torn when the pad is cleaned by bristles of a brush type conditioning apparatus that is used to remove polishing debris and to condition the polishing layer. The bristles are urged to intrude into the pores, and sometimes to intrude into the pressure sensitive adhesive that secures the polishing layer to an underlying base layer of the polishing pad. The pores transport slurry during a polishing operation. Tearing of the polymer bordering the pores creates keyholes that lose an ability of the pores to hold slurry during a polishing operation. Tearing is severe enough in some areas of the polishing layer that the polishing layer is torn away from the underlying layer. Consequently, the polishing pad has a reduced useful life, caused by the brush type conditioning apparatus.
What is desired is a conditioning apparatus that fits with a known polishing machine, and that utilizes a ring gear and a sun gear of the known polishing machine to drive the conditioning apparatus without a requirement for modification of the conditioning apparatus.
The present invention does not use bristles that cause the tearing of the pore walls and therefore does not reduce the useful life of the polishing pad.
According to the invention, a conditioning disk is fabricated from a unitary circular plate formed with gear teeth along its circular edge, and formed with block form protrusions on at least one of two opposite major surfaces of the plate, which protrusions are impelled in a sweeping motion by rotation of the unitary plate as a planetary gear in meshed engagement with a sun gear and a ring gear of a polishing apparatus.